God is Perfect, capital "P".

Something that was perfect continuously is more nearly perfect than something that had to change to become perfect, since it was perfect for more time, and has no history of imperfection. Therefore, any omnimax deity cannot be trans, as it implies changing states, when changing states from (or to) Perfection means non-perfection exists within the entity.

"God is hermaphroditic" could have a of logic-based argument, since God is Everything, but their argument is just... heresy for the sake of heresy, endorsed by a church.